Gel-based air freshener products have been formulated from (i) an aqueous medium containing a volatile air freshener (odorizer or deodorizer) component, and (ii) an agent which gels the aqueous medium. In operation, the volatile air freshener components are continuously released from the gel by room temperature evaporation of the aqueous medium within the gel. Volatile air freshener components can include volatile oils which provide a pleasant odor and/or mask unpleasant odors, as well as disinfectants, bactericides and insecticides.
The formulations of many gel-based air fresheners utilize carrageenan as a gelling agent. For example, British Patent Specification No. 1,241,914 (published Aug. 4, 1971) discloses a biocidal and/or deodorizing composition which includes 1-6 percent of a gelling agent, and 99-94 percent of an aqueous medium containing the active biocidal and/or deodorizing agents, which in turn represent 1-10 percent of the gel. The gelling agent is a mixture of the kappa and iota fractions of carrageenan, in ratio of 1.5:1-7:1, respectively.
M. Lanzet (U.S. Pat. No. 2,927,055, issued Mar. 1, 1960) discloses an air treating gel composition which consists essentially of 97-98 percent of an aqueous medium, of which 1-10 percent are "air treating components" including a mixture of essential oils, and about 2-3 percent of an aqueous gelling agent. In terms of weight percentage of the complete gel formulation, the aqueous gelling agent is formed from 0.75-1.8 percent carrageenan, 0.2-0.75 percent locust bean gum, 0.1-0.75 percent potassium chloride, and 0.15-0.7 percent sodium carboxymethyl-cellulose.
Lin (U.S. Pat. No. 4,056,612, issued Nov. 1, 1977) discloses an air freshener gel consisting essentially of about 1.5-4 percent of a gelling agent, and 98.5-96 percent of an aqueous medium containing a volatile air freshener component. The three-component gelling agent contains at least 40 percent carrageenan, 0.6-2 percent kappa carrageenan, 0.2-1 percent locust bean gum, and 0.05-1 percent of a water soluble ammonium salt having a pH greater than 5.0. The disclosed compositions may also contain co-solvents, such as ethanol, isopropanol, ethylene glycol, propylene glycol, hexalin glycol, or cellosolve; bactericides or fungicides; dyes; or emulsifiers.
A recurring problem with the solid air freshener compositions based primarily on carrageenan as the gelling agent is syneresis, i.e., the loss of moisture from the gel to the surface, thus giving the gel a wet appearance. More specifically, syneresis results in a separation of the aqueous medium from the gel, due to gel contraction and/or inadequate water gel strength. Attempts to alleviate the syneresis problem have included incorporating various metal ions into the gels, and using carboxymethylcellulose (CMC) instead of carrageenan as the primary gelling agent.
For example, Singleton et al. (U.S. Pat. No. 3,997,480, issued Dec. 14, 1976) discloses a CMC-based gel composition, including an aqueous medium, a volatile air treating component, and a gelling agent, which consists of the reaction product of a 1-10 percent water soluble cellulose derivative, with or without modifying gums, and a metal salt having a low solubility in water. The addition of the salt to the aqueous solution of cellulose derivative is disclosed as affecting the water solubility of the cellulose derivative, so that the metal salt of the cellulose derivative is precipitated slowly and in a controlled fashion to form the gel.
Sayce et al. (U.S. Pat. No. 3,969,280, issued July 13, 1976) discloses an air freshener gel comprising water, from 0.5-10 percent of sodium or potassium CMC, 0.05-10 percent of a surfactant, 0.01-10 percent of a perfume, and a source of a trivalent metal cation selected from aluminum ions and chromic ions, in an amount sufficient to give a ratio of CMC to effective weight of trivalent cation of 1:0.01 to 1:0.1. The disclosed surfactant may be a nonionic or cationic surfactant; anionic surfactants are disclosed to be unsuitable because they interfere with the formation of gel structure. Additionally, surfactant gum-like materials, e.g., nonionic hydrocolloids, may be utilized as the surfactant. Optional ingredients can include a sequestering agent, a solvent, preservatives, dyes or colorings.
Consumer acceptance of many commercially available gel-based air freshener products has been hampered because progressive evaporation of the active substances therein can cause these products to lose their shape, or to shrink or disintegrate, eventually leaving a shapeless, shrunken and dried residue. Moreover, the reduction in surface area caused by the collapse of the gel matrix effectively reduces the rate of fragrance release; i.e., the effective fragrance-releasing surface area of these products decreases over time. Art workers have attempted to alleviate these problems by forming air fresheners from paraffin, which is a solid at room temperature, and metal soaps which gel the paraffin, such as aluminum monostearate, distearates and/or tristearates. Disadvantageously, the evaporation rate of these formulations, which affects the length of time needed to distribute the active substance within a given space and to eliminate an undesirable odor in that space, is reduced to the evaporation rate of the active substance in the product, so that it is not possible to substantially increase or decrease the rate of evaporation.
Hautmann (U.S. Pat. No. 4,117,110, Sept. 26, 1978) discloses an air improving composition which purports to address this problem by utilizing a liquid paraffin having a suitable evaporation number, in order to vary the evaporation rates of the active ingredients. The Hautmann composition comprises 5-30 percent of a carrier material consisting essentially of sodium stearate; 30-80 percent of a paraffin agent consisting of a liquid paraffin, which at 20.degree. C., has an evaporation number ranging from 8-1000, based on an evaporation number for diethylether at 20.degree. C. of 1; a sufficient amount of water to form a solid gel; and a deodorant agent and/or an odorant agent, or a mixture thereof.
Another disadvantage of known gel-based air freshener systems is temperature instability. For example, carrageenan-based systems have exhibited a lack of stability when exposed to the extreme temperatures frequently encountered during storage and/or shipping in the summer and winter months. Such lack of stability is exhibited by one or more of the following: product weight loss, deterioration of product appearance, loss of effectiveness, and the like. Specifically, the poor freeze-thaw stability of such carrageenan-based compositions is shown in that samples which return to ambient from temperatures below about -20.degree. C. exhibit a significant fluid loss, and corresponding reduction in size and appearance. Other gel compositions which utilize soaps, and more specifically stearates, as gelling agents, e.g., sodium or potassium salts of stearic acid, also exhibit poor temperature stability, especially at high temperatures. For example, samples which are returned to ambient temperatures after having been exposed to temperatures of above about 48.degree. C. lose their integrity completely, and liquify.
In an attempt to solve the problems of high- and low-temperature stability, Streit et al. (U.S. Pat. No. 4,178,264, Dec. 11, 1979) utilized a blend of carrageenan and stearate salt as a gelling agent. The air treating gels disclosed by Streit et al. comprise 1.5-15 percent of a 0.3:1 to 5:1 weight ratio of carrageenan and stearate salt; from 0.5-6 percent of essential oils and aromatics, from 1.0-20.0 percent of a solvent component; and the balance water. Suitable stearates may include sodium and potassium stearates as well as alkanolamines. The solvent component may include glycols such as ethylene glycol, liquid polyethylene glycols having a molecular weight from about 200-600, solid polyethylene glycols having an average molecular weight from about 1000-7500, ethylene and polyethylene glycol monomethyl ethers, and C.sub.2 -C.sub.18 alcohols.
British Patent Specification No. 1,598,449 (published Sept. 23, 1981) discloses air-freshening gels which are stearate-based, or "soap"-gels, in contrast with water-based gels. The disclosed soap-gels form a substantially rigid composition which contains: (1) a soap, such as sodium stearate; (2) an alcoholic medium comprising a monoalkyl ether of an alkaline glycol; and (3) one or more volatile air treating components.
In addition to gel-based compositions, plastic foam-based structures have also been utilized as air fresheners. For example, "in-situ" impregnation of polyurethane foams has been accomplished by adding ingredients such as room deodorizers to the foam reactant phase during the production or foaming process. However, polyurethane foam systems formed by "in situ" techniques are disadvantageous in that the amount of active ingredients that can be added to the initial foam reactant mix is limited. Additionally, many polyurethane foaming systems involve exothermic reactions which may generate excess heat or cause adverse chemical reactions to occur. Such reactions may be especially harmful to heat-sensitive fragrances.
Palinczar et al. (U.S. Pat. No. 4,339,550, issued July 13, 1982) discloses a hydrophilic foam impregnated with volatile organic ingredients. The composition may be formed "in-situ" by reacting 5-85% of a capped polyoxyethylene polyol prepolymer with 5-75% of water and 0.1-25% of the volatile organic ingredient. From 1-40% of a surface active agent, and 5-80% of a "control release ingredient" intended to control the release rate of the volatile component, may also be included in the foam. The "control release" ingredient may include, e.g., gums such as hydroxpropylmethyl-cellulose, sodium carboxymethylcellulose and karaya gum.
Commonly-assigned U.S. Pat. No. 4,581,385 to Smith et al. discloses the preparation of foams useful as carpet cleaning compositions. The foams are formed by foaming a polyurethane prepolymer resin with an aqueous reactant phase comprising a slurry of solid abrasive particles and a surfactant. The disclosed reactant phase may optionally contain a minor amount of a volatile odoriferous agent which is chemically compatible with the surfactant, in order to deodorize carpet and freshen room air. The foam is cured to form a bun having a tensile strength of less than about 10 p.s.i., which is subsequently shredded to form foam particles having a size of about 5-20 mesh.
As mentioned above, difficulties have been encountered in attempts to control the release rate of volatile air freshener ingredients. For example, commercially available solid (gel- or paraffin-based) air fresheners are "first-order" systems; i.e., characterized by a "first-order" evaporation rate of their volatile components. In first-order evaporation, evaporation is initially high, but rapidly levels off to an ineffective amount. Thus, consumers who use the solid products have found that they are too strong at first, but quickly become barely noticeable.
In contrast to the solid systems, liquid air freshener products are known which may achieve the desired "zero-order" release rate. These products utilize a wick device to gradually draw up a fragrant liquid from a reservoir, and thus may steadily release the fragrance as long as the liquid lasts. Disadvantageously, these liquid systems utilize large amounts of the active ingredients in a short amount of time, and are thus correspondingly more expensive. Further, ease of use is less with liquid products than with solid products, because the liquid ingredients may easily be spilled. If spilled, the liquid ingredients may damage the surface on which the product was placed.
Therefore, a need exists for an air freshener product which is long-lasting, convenient to use, and which can achieve a sustained release rate of the volatile air freshening ingredients therein.